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Logical positivism


Logical positivism (later referred to as logical empiricism, rational empiricism, and also neo-positivism) is a philosophy that combines positivism with formal logic.

The term "logical positivism" itself originated in the Vienna Circle in the 1920s, where Rudolf Carnap, Otto Neurath, et al. divided statements into those which are analytic (true a priori, i.e. true before empirical experience) and those which are synthetic (true a posteriori, i.e. verified by sensory experience). German philosopher Immanuel Kant (1724-1804) had made a fourfold distinction between analytic and synthetic statements, and a priori and a posteriori ones, and had declared that there were some synthetic a priori statements (everyone agreed on the existence of analytic a priori and synthetic a posteriori statements, and on the non-existence of analytic a posteriori ones); the logical positivists denied the existence of any such synthetic a priori statements and held that all a priori statements are analytic. So, according to the logical positivists, there are only two kinds of statements, analytic and synthetic, with all the first being a priori and all the second being a posteriori.

Logical positivism held that philosophy should aspire to the same sort of rigor as science. Philosophy should provide strict criteria for judging sentences true, false and meaningless, and this judgment should be made by the use of formal logic coupled with empirical experience.

Examples of logical positivists include Moritz Schlick, Rudolf Carnap, Otto Neurath, Friedrich Waismann, Bertrand Russell, and A.J. Ayer. Karl Popper is also often associated with the Vienna Circle, although he was never a member, and he went on to become a main critic of positivism's "verification" with his own "falsification" approach. Otto Neurath claimed that the most significant output produced by the logical positivist circle was the International Encyclopedia of Unified Science published by University of Chicago Press in 1938. Most of these authors contributed to this encyclopedia.

Historical Background

Positivism itself goes back to the nineteenth century and possibly even earlier. William Reese has written that positivism is "A family of philosophies characterized by an extremely positive evaluation of science and scientific method. In its earlier versions, the methods of science were held to have the potential not only of reforming philosophy but society as well. Later versions have concentrated on the reform of philosophy" (Dictionary of Philosophy and Religion, New and Enlarged Edition, 596).

The terms "positivism" and "positive philosophy" were introduced by French philosopher Saint-Simon (1760-1825) for his scientific approach to the world, along with the implications of this approach for ethics, religion, and politics. August Comte was a disciple of and collaborator with Saint-Simon from 1817 to 1824, and Comte popularized use of the term.

The most important and influential of the positivists for subsequent philosophical developments was Ernst Mach (1836-1916). Mach, a physicist-philosopher, had been influenced by George Berkeley, David Hume, and Hermann von Helmholtz. Mach held that that all scientific concepts must be understood as summaries of sense experience, and his goal was to rid science of all unobservables. Mach's work was admired by the members of the Vienna Circle and was a chief influence on them; in fact they originally called themselves the Ernst Mach Society.

Logic had been investigated for some 2,500 years in both Western and Eastern thought. In the nineteenth and twentieth centuries there was a great burst of interest in and further development of the fields of logic, set theory, and logical systems. Some of the many contributors to these developments were George Boole, John Venn, C.S. Peirce, Augustus De Morgan, Ludwig Wittgenstein, George Cantor, Giuseppe Peano, Alfred North Whitehead, Bertrand Russell, Alonzo Church, Willard van Orman Quine, Rudolf Carnap, and Alfred Tarski.

Those developments in logic were the second leg of the combination that became logical positivism. This strong wedding of logic to positivism distinguished the logical positivists from their predecessors.

Assertions and Origins of Logical Positivism

Although the logical positivists held a wide range of beliefs on many matters, they all shared an interest in science and deep skepticism of the theological and metaphysical. Following Wittgenstein, many subscribed to the correspondence theory of truth, although some, like Neurath, believed in coherentism. They believed that all knowledge should be based on logical inference from simple "protocol sentences" grounded in observable facts.

The logical positivists were very much influenced by and were great admirers of the early Ludwig Wittgenstein (from the period of the Tractatus). Wittgenstein himself was not a logical positivist, although he was on friendly terms with many members of the Vienna Circle while in Vienna, especially fellow aristocrat Moritz Schlick. However, Wittgenstein's relations were not entirely amicable after he left Vienna. While Wittgenstein worked mostly in cooperation for nearly a decade with Circle member Friedrich Waismann to impose form and structure on his often oracular utterances, using him as a secretary and speaking of cooperating on a book with him, when Waismann came to Cambridge in 1937 Wittgenstein barely acknowledged him.

Logical positivism is perhaps best known for the verifiability criterion of meaning, which asserts that a statement is meaningful if and only if it is empirically verifiable. One intended consequence of the verification criterion is that all non-empirical forms of discourse, including ethics and aesthetics, are not "literally" or "cognitively" meaningful, and so belong to "metaphysics". The most succinct and influential statement of this position-at least in the English-speaking world-was expressed in Alfred Jules Ayer's book, Language, Truth, and Logic.

Logical positivism was essential to the development of early analytic philosophy. It was disseminated throughout the European continent and, later, in American universities by the members of the Vienna Circle. A. J. Ayer is considered responsible for the spread of logical positivism to Britain. The term subsequently came to be almost interchangeable with "analytic philosophy" in the first half of the twentieth century. Logical positivism was immensely influential in the philosophy of language and represented the dominant philosophy of science between World War I and the Cold War. Many subsequent commentators on "logical positivism" have attributed to its proponents a greater unity of purpose and creed than they actually shared, overlooking the complex disagreements among the logical positivists themselves.


Critics of logical positivism say that its fundamental tenets could not themselves be formulated in a way that was clearly consistent. The verifiability criterion of meaning did not seem verifiable; but neither was it simply a logical tautology, since it had implications for the practice of science and the empirical truth of other statements. This presented severe problems for the logical consistency of the theory. Another problem was that, while positive existential claims (there is at least one human being) and negative universals (not all ravens are black) allow for clear methods of verification (find a human or a non-black raven), negative existential claims and positive universal claims do not.

Universal claims could apparently never be verified: How can you tell that all ravens are black, unless you've hunted down every raven ever, including those in the past and future? This led to a great deal of work on induction, probability, and "confirmation," (which combined verification and falsification; see below).

Karl Popper, a well-known critic of logical positivism, published the book Logik der Forschung (English: The Logic of Scientific Discovery) in 1934. In it he presented an influential alternative to the verifiability criterion of meaning, defining scientific statements in terms of falsifiability. First, though, Popper's concern was not with distinguishing meaningful from meaningless statements, but distinguishing scientific from metaphysical statements. He did not hold that metaphysical statements must be meaningless; neither did he hold that a statement that in one century was metaphysical, while unfalsifiable (like the ancient Greek philosophy about atoms), could not in another century become falsifiable, and thus scientific (by the twentieth century, atoms would become part of science). About psychoanalysis he thought something similar: in his day it offered no method for falsification, and thus was not falsifiable and not scientific, but he didn't exclude it being meaningful, nor did he say psychoanalysts were necessarily wrong (it only couldn't be proved either way: that would have meant it was falsifiable), nor did he exclude that one day psychoanalysis could evolve into something falsifiable, and thus scientific. He was, in general, more concerned with scientific practice than with the logical issues that troubled the positivists. Second, although Popper's philosophy of science enjoyed great popularity for some years, if his criterion is construed as an answer to the question the positivists were asking it turns out to fail in exactly parallel ways. Negative existential claims (There are no unicorns) and positive universals (all ravens are black) can be falsified, but positive existential and negative universal claims cannot.

Logical positivists' response to the first criticism is that logical positivism, like all other philosophies of science, is a philosophy of science, not an axiomatic system that can prove its own consistency (see Gödel's incompleteness theorem). Secondly, a theory of language and mathematical logic were created to answer what it really means to say things like "all ravens are black."

A response to the second criticism was provided by A. J. Ayer in Language, Truth and Logic, in which he sets out the distinction between 'strong' and 'weak' verification. "A proposition is said to be verifiable, in the strong sense of the term, if, and only if, its truth could be conclusively established by experience" (Ayer 1946, 50). It is this sense of verifiable that causes the problem of verification with negative existential claims and positive universal claims. However, the weak sense of verification states that a proposition is "verifiable… if it is possible for experience to render it probable." After establishing this distinction, Ayer goes on to claim that "no proposition, other than a tautology, can possibly be anything more than a probable hypothesis" (Ayer 1946, 51) and therefore can only be subject to weak verification. This defense was controversial among logical positivists, some of whom stuck to strong verification, and claimed that general propositions were indeed nonsense.

Subsequent philosophy of science tends to make use of the better aspects of both of these approaches. Work by W. V. O. Quine and Thomas Kuhn has convinced many that it is not possible to provide a strict criterion for good or bad scientific method outside of the science we already have. But even this sentiment was not unknown to the logical positivists: Otto Neurath famously compared science to a boat that we must rebuild on the open sea.

See also

  • Vienna Circle
  • Kurt Gödel
  • Rudolf Carnap
  • Moritz Schlick
  • Otto Neurath
  • David Stove


There is a huge literature, running to many hundreds of items, on logical positivism, the Vienna Circle, and topics associated with each of those. Here we can list only a few examples:

  • Ayer, A. J. Language, Truth and Logic. London: Gollancz, 1936; 2nd ed, 1946.
  • Ayer, A. J. Logical Positivism. New York: Free Press, 1959.
  • Edmonds, David and John Eidinow. Wittgenstein's Poker. New York: HarperCollins Publishers Inc., 2001.
  • Neurath, Otto, Rudolf Carnap, et. al. International Encyclopedia of Unified Science. Chicago: University of Chicago Press, 1938.

External Links

All links retrieved July 24, 2018.

General Philosophy Sources